With the emergence of the nanotechnology era, the capacity to take extremely accurate measurements in order to control the production, operation and ageing of different components on a nanometric scale has become essential. Recurring problems are thus the re-localisation and co-localisation of measurements taken at different instants of time and/or with different measuring instruments. As an example, different types of measurements can be optical microscopy, Raman microscopy, electron microscopy measurements forming an image of the sample with a micrometric or sub-micrometric spatial resolution.
In the present document, by accuracy in position and/or in orientation, this means both the notion of absolute accuracy and repeatability.
By re-localisation of measurements, here this means the possibility of taking measurements in one same place of a sample at different instants in time, the sample possibly having undergone a certain physical, chemical or other treatment between a plurality of measurements. The re-localisation accuracy currently requested depends on the structure of the sample and on the spatial resolution of each type of measurement, but is situated generally in the micrometric, sub-micrometric or nanometric scale.
By co-localisation of measurements, here this means the possibility to take different measurements in one same place of a sample, each measurement giving complementary information with respect to the other measurements. For example, the different measurements can be based on a physical or chemical contrast and/or a different spatial resolution.
The re-localisation and the co-localisation of measurements firstly require a high spatial accuracy since here it is the accuracy of the positioning of an incident beam and/or a detection system with respect to the sample to take a localised measurement. The re-localisation and the co-localisation of measurements secondly require a high repeatability of measurements. Indeed, it is essential to be able to repeat a measurement under identical conditions and to obtain the same result on a stable sample. These conditions of accuracy and repeatability are essential to make it possible to transfer the sample to analyse it by different techniques.
The problems of re-localisation and co-localisation of measurements can be returned to those of a transfer of a system of reference coordinates to the system of coordinates of the measuring instrument. In this field, today there is a plurality of solutions.
A characterisation device is known, for example, from document U.S. Pat. No. 7,630,628, including a positioning system making it possible to position the measuring instrument with respect to the sample to characterise in one localised measuring point of the sample. The positioning system from document U.S. Pat. No. 7,630,628 includes, in particular, a sample stage on which the sample is placed, the controlling means making it possible to move this stage accurately and in a repeatable manner. This makes it possible, if the sample is secured to the sample stage, and if the sample is not handled between two measurements being taken, to take two measurements at two substantially identical measuring points. However, the positioning system from document U.S. Pat. No. 7,630,628 does not make it possible to know the position of the measuring instrument with respect to the sample, i.e. to absolutely position the measuring instrument with respect to the sample.
Patent document US 2013/0077160 A1 describes an alignment marking unit for a sample stage of an imaging microscope. The alignment marking unit includes one or more geometric or alphanumeric patterns, of different sizes, for example L-shaped. The pattern advantageously has a rotation asymmetry and natural perpendicular axes defining the orientation of a reference system of coordinates. To define the reference system of coordinates, the operator must position, manually or automatically, a pattern at a suitable scale according to the imaging system. This device requires an accurate and often laborious pre-positioning. The localisation accuracy is limited by the pixel size and by the resolution of the imaging and image processing system. In addition, the accuracy in angular orientation is limited, of around Δα ˜10−2 radian. This angular accuracy limitation induces positioning errors according to the distance between the alignment mark and the sample: at a distance d˜5 mm, the positioning error is proportional to d Δα ˜50 microns, which is insufficient in applications on a microscopic scale.
Patent document US 2012/0133757 A1 describes a sample stage device that can be adapted on the translation stage of an optical microscope and of an electron microscope. The sample stage includes three alignment marks of geometric shape that are visible to the naked eye and remote from one another. The three alignment marks define a reference marker connected to the sample stage. An imaging system and an image processing system make it possible to recognise the position and the orientation of the alignment marks and to determine a system of reference coordinates. Zones of interest of the sample can be referenced in this system of reference coordinates and can be found later on the same instrument or on another instrument, while the sample remains secured to the sample stage supporting the alignment marks. However, this system requires an accurate manual pre-positioning to bring each alignment mark into the field of view of the imaging system. The smaller the alignment mark is with respect to the size of the sample, the more laborious the pre-positioning is. In addition, this system is limited to a restricted magnification range: if an alignment mark is suitable for a certain instrumental field of view, the instruments with a magnification which is too small cannot distinguish it, and the instruments with a magnification which is too large, cannot form a full image from it. Moreover, this system offers a localisation accuracy of around the pixel size of the imaging system. Indeed, during manual marking, the accuracy is conditioned by the action of the operator and does not exceed the size of a pixel. In the case of automatic marking, the patterns used make it possible to mark the position thereof with an accuracy of around one pixel. Furthermore, this system requires the use of at least three alignment marks separated spatially, the distance between the alignment marks determining the angular accuracy in each direction of the system of coordinates. This device is consequently bulky, as the three alignment marks are arranged far from the sample. Finally, this device can be sensitive to the thermal dilatation effects of the support which induce a positioning error and limit the accuracy of this device.
Finally, from patent document FR 2993988, an alignment sight secured to the rear face of a sample is known. An optical imaging system forms an image of the alignment sight. An image processing system provides from this image with the sight, the position and the orientation of the sample with respect to a measuring instrument, subject to calibration of the measuring instrument with respect to the imaging system. However, this alignment sight is not suitable for very different magnifications. Patent document FR 2993988 also discloses a multimodal and multiscale marker including a pattern of self-similar structure not having rotation symmetry, formed by a metal deposit on a glass slide. On the one hand, this marker has an optical contrast making it possible for it to be observed in optical microscopy at different magnifications and is therefore a multiscale marker. On the other hand, this marker has a topographical structure making it possible for it to be observed in electron microscopy which makes it multimodal. However, the accuracy of positioning and orientation of this multimodal and multiscale marker is fundamentally limited by the size of a pixel.
Document US 2016/124431 A1 describes a multiscale marking device including embedded markers. Document US 2014/049818 A1 describes a microscope slide including reference points arranged at predetermined places.
One of the aims of the invention is to propose a device and a method making it possible for co-localisable measurements on a nanometric scale for a great variety of measuring instruments in order to produce a multimodal characterisation of a sample, i.e. to analyse this sample on a nanometric scale by different techniques.
Another aim of the invention is to make it possible for re-localisable measurements in one same place of the sample with a sub-micrometric or nanometric accuracy to produce measurements at different instants of time or to produce a multiscale characterisation centred on the same place of the sample, for example via a microscope with different magnifications.